Pull Request: Split showContextMenu_ (#2581)
Pull Request: Split showContextMenu_ (#2581)

* Split showContextMenu_

Split showContextMenu_ into generateContextMenu_ and showContextMenu_. This allows for custom Blockly forks to easily extend the context menu options available on all blocks by just doing something like

```
var oldGenerateContextMenu_ = Blockly.BlockSvg.prototype.generateContextMenu_;
Blockly.BlockSvg.prototype.generateContextMenu_ = function() {
  var menuOptions = Blockly.BlockSvg.prototype.generateContextMenu_() || [];
  // Push other options into menuOptions
  return menuOptions;
}
```

Rather than having to modify the core code in such a way as to cause unnecessary maintenance overhead when upgrading Blockly versions.

* Forgot the docblock, sorry

* Oops, missed a few ESLint things

* Update block_svg.js

Updated to be protected rather than private.

joshlory/blockly,rachel-fenichel/blockly,nickmain/blockly,joshlory/blockly,nickmain/blockly,rachel-fenichel/blockly,rachel-fenichel/blockly,nickmain/blockly,picklesrus/blockly,nickmain/blockly,google/blockly,picklesrus/blockly,picklesrus/blockly,joshlory/blockly,rachel-fenichel/blockly,google/blockly,google/blockly,rachel-fenichel/blockly,rachel-fenichel/blockly,google/blockly,google/blockly,google/blockly,mark-friedman/blockly,mark-friedman/blockly,rachel-fenichel/blockly,nickmain/blockly,google/blockly,nickmain/blockly,mark-friedman/blockly,mark-friedman/blockly,mark-friedman/blockly,mark-friedman/blockly